The processing of photographic film in a processor or processing assembly involves a series of steps such as developing, bleaching, fixing, washing and drying. These steps lend themselves to mechanization by conveying a continuous web of film or cut sheets of film or photographic paper sequentially through a series of processing stations or processor tanks which make up the processor, each one containing a different processing solution appropriate to the process step at that station. Typical drive systems for processors are designed to provide on-demand power to each or any of roller systems which are located in each of the processor tanks for conveying photosensitive material. For some processors, the film path through which the film travels can be described as a spiral path through the various tanks with the number of turns through each of the tanks being determined by the particular process in the tank. Due to this variation, as well as a difference in wet film stretch, the action of flex hubs, mechanical binding, rubbing, etc., each tank of a processor typically places different tension load demands onto that portion of the processor. The various tension loads coupled with low operating tension allowances desired by current processors indicates the need for an on-demand drive system between each of the processing tanks.
On-demand drive systems are typically defined as any system that has a pacer roller located at the take-up end of the processor. This pacer roller is the only film roller that is constantly positively driven. The other rollers can be idler-style rollers that provide positive drive only when that portion of the film web exceeds the design film tension.
A film transport rack system for each processor tank of a typical processing system will have a constant turning drive roll, which is regulated to a speed that is generally about 5% to 15%, typically 5% to 8%, faster than the speed provided by the pacer roller. In this system, the pacer roller determines the rate of speed that the film should travel through the tank, dryer and take-up system. In theory, the film could be pulled through the various tank/rack systems, then be fed through an exit elevator, then onto a take-up reel. Unfortunately, the web tension of the film would most likely be too great at different points along the film path and additional driving is needed at various (and changing) positions, at intermittent time periods.
One proposed solution is to use a spring mounted roller hub (flex hub drive) within the tank that allows the roller hub to be pulled down to engage a constant speed drive roller assembly when that particular section of the film web is undergoing high tension. The amount of allowable tension can be varied in gross amounts by using different tension spring hubs and tuning can be accomplished by the use of adjusting rods on the film hub axis. Adjusting the spacing or gap of the roller hub further away from the drive roller increases the required tension level to engage the drive while narrowing the spacing or gap decreases it. However, this approach has a drawback in that as you proceed further upstream from the pacer roller located at the end of the take-up end of the processor, there is a greater intermittent film motion mainly caused by the cumulative effect of changing center lines caused by the action of flex hubs, which contributes to increase the tension loads.
Recent designs require that photoprocessing film be subject to relatively light film tensions, and that a fine control of film motion be achieved at a certain point of the processing path, such as at a blue exposure lamp housing of a KODACHROME film processing lab, an ink jet machine, an air flow coating mechanism, etc. The speed of the film at the blue exposure lamp housing or any of the elements noted above needs to be finely controlled since an increase in residence time of the film in a vicinity of the blue exposure lamp housing or any of the elements noted above will adversely affect film development. Conventional assemblies do not provide for a fine control of film motion at a specific point, such as, a blue exposure lamp housing of a processor which is typically at an intermediate location of the processing path of the processor.
Typically, as explained above, to regulate proper low film tension, a flex hub drive is used which allows the film to travel over a series of roller assemblies in an idler roller mode when the film is under low tension. Under higher tension conditions the flex hubs deflect the roller assembly until the roller contacts a constantly turning overdrive roller which provides additional assist to the drive system. When the high tension condition is relieved, the flex hubs return the roller assembly to its idler roller position. However, as noted above, this kind of system does not provide for a fine control of the motion of the film at an intermediate portion of the processing assembly. This is detrimental in, for example, KODACHROME processing in which low tension is desired because the processing involves stapling or splicing multiple films together, and in which a blue exposure lamp housing is typically provided in an intermediate location of the photoprocessing system where a precise film speed control and motion is desired to prevent over-exposure.
An arrangement such as shown in U.S. Pat. No. 4,967,222 uses two motors to regulate the film speed through a large processing tank in which the film path length is variable. This arrangement monitors the speed of a web at the inlet of the tank, and uses this monitored speed to regulate the speed of advancing rolls at the outlet of the developing tank in such a way that the speeds match. However, this system is not concerned with a monitoring of film tension and a control of a secondary drive provided downstream of a primary drive based on the monitored tension in a vicinity of the primary drive.